The present invention relates to a magnetic disc device used in computers, information storage devices and so on, a magnetic storage device used in such information home appliances as digital VTRs, and a magnetic recording, and and, more particularly, to a magnetic recording and reading device suitable for realizing high-speed recording and reading, and for high-density recording.
Semiconductor memories, magnetic memories etc., are used in the storage or recording devices of information equipment. Semiconductor memories are used in internal primary storage in the light of high-speed accessibility and magnetic memories are used in external secondary storages in the light of a high capacity, low cost and nonvolatile property. Magnetic disk devices, magnetic tapes and magnetic cards are the main current in the magnetic memories. A magnetic recording portion which produces a strong magnetic field is used in order for writing magnetic disks, magnetic tapes or magnetic cards. Further, reading portions based on the magnetoresistance effect or the electromagnetic induction effect are used in reading magnetic information recorded at a high density. In recent years, for reading, the giant magnetoresistance effect and the tunneling magnetoresistive effect have also begun to be examined. These functional portions for recording and reading are both installed in an input-output part which is called a magnetic head.
The basic configuration of a magnetic disk device is shown in FIGS. 10A and 10B. FIG. 10A shows a plan view of the device and FIG. 10B shows a vertical-sectional view of the device. Recording media 101-1 to 101-4 are fixed to a hub 104 to be rotated by a motor 100. In FIG. 10B shows one example which comprises four magnetic disks 101-1 to 101-4 and eight magnetic heads 102-1 to 102-8. However, the magnetic disk device may comprise at least one magnetic disk and at least one magnetic head. The magnetic heads 102-1 to 102-8 move on the rotating recording media. The magnetic heads 102-1 to 102-8 are supported by a rotary actuator 103 via arms 105-1 to 105-8. Suspensions 106-1 to 106-8 have function of the pressing the magnetic heads 102 against the recording media 101-1 to 101-4 under a determined load, respectively. A given electric circuit is needed for processing of reproduction signals and for inputting and outputting of information. Recently, a signal processing circuit in which waveform interference at high-density is positively utilized, such as PRML (Partial Response Maximum Likelihood) or EPRML (Extended PRML) which is an enhanced PRML, has been adopted, contributing greatly to a high-density design. The signal processing circuit is installed in a circuit board on a cover 108, etc.
The functional portion for writing and reading information on a magnetic head assembly is comprises components shown in FIG. 11A, for example. A writing portion 111 is comprised of a spiral coil 116 between magnetic poles 117, 118 which are magnetically connected with each other. The magnetic poles 117, 118 are both composed of a magnetic film pattern, which are made of an NiFe alloy, etc., respectively. The reading portion 112 comprises a magnetoresistance element 113 made of an NiFe alloy, etc. and an electrode 119 for applying a constant current or a constant voltage to the element 113 and for detecting changes in resistance. The magnetic pole 118, which is made of an NiFe alloy, etc. and serves also as a magnetic shielding layer, is provided between the writing and reading portions. There is further a shielding layer 115 underneath the magnetoresistance element 113. A reading resolution is determined by the clearance distance between the shielding layer 115 and the magnetic pole 118 (serving also as another shielding layer). The functional portion is formed on a magnetic head slider 1110 (FIG. 11B) via an underlayer 114 made of Al2O3, etc. Incidentally, the magnetic head slider, which is provided with a protection layer made of hard-carbon, etc. on the surface opposed to the magnetic recording medium, is supported by a gimbal 1111 and a suspension 1113, as shown in FIG. 11B. The magnetic head slider moves relatively to the magnetic recording medium while floating from the medium surface and, after positioning in an arbitrary position by an arm 1114 connected to a motor, realizes the function of writing or reading magnetic information via lead lines 1116 and 1115. With respect to the above function, there is also provided an electric control circuit together with the aforementioned signal processing unit or on the head carriage.
A detailed structure of a recording medium is schematically shown in FIG. 12. As described in JP-A-3-16013, most of the conventionally used recording media are produced by forming a magnetic layer 123 made of a Coxe2x80x94Crxe2x80x94Ta alloy, or a Coxe2x80x94Crxe2x80x94Pt alloy, etc. on a non-magnetic substrate made of Al plated with an NiP alloy, a glass, a high-hardness ceramics, a polished Si or the like, or a plastic substrate 121 by the sputtering method, or the evaporation method, or the plating method, etc. Usually, an under layer 122 made of Cr, or a Cr alloy, etc. for orientation control of the magnetic layer is often formed on the substrate. Furthermore, a protection film 124 made of diamond-like carbon containing nitrogen and/or hydrogen, or SiO2 or SiN or ZrO2, etc. is provided to ensure durability of sliding resistance, and a lubricating film 125 made of perfluoro alkyl polyether having an adsorptive or a reactive end group, or organic fatty acids, etc. is provided.
In addition to the magnetic recording device, magneto-optic recording devices that perform recording and reading on a magnetic recording medium through the use of light have also been put to practical use. The magneto-optic recording devices are classified into one type in which recording is performed only by light modulation and another type in which recording and reproduction are performed by light with a modulated magnetic field. However, the both types greatly rely on heat when recording and reading. Therefore, according to such type of devices, it is impossible to perform recording and reading in high data transfer rate and thus they have been adopted mainly in backup systems, etc.
The importance of a storage device is determined by its storage capacity and the speed during inputting-outputting operations. In order to increase competitiveness of products, it is necessary for the storage device to increase capacity by higher recording density, higher rotational speed and higher data transfer rate than those of the prior art. Thus, an important problem to be solved by the present invention is to provide a device capable of recording and reading at a high data transfer rate of not less than 50 MB/s and, more preferably, that at a high density of not less than 5 Gb/in2. A magnetic recording medium capable of recording and reading at a high frequency and capable of obtaining a high S/N ratio at a high density and a magnetic head capable of generating a sufficient magnetic recording field at a high frequency are necessary for meeting the requirement.
In conventional magnetic recording media, there have been proposed and actually carried out to reduce noise by refining crystal grains in order to obtain a high S/N ratio at a high density of about 1 to 3 Gb/in2, and by promoting segregation of non-magnetic components at grain boundaries to reduce exchange coupling among crystal grains as being taught in JP-A-63-148411, JP-A-3-16013 and JP-A-63-234407 so as to make the coercive squareness S* to not more than 0.85 and the rotational hysteresis loss RH to the range of 0.4 to 1.3. Noise can be considerably reduced by recording and reading at a data transfer rate of not more than about 20 MB/s. However, when the magnetic recording was carried out on that film media of the prior art at a high frequency of not less than 50 MB/s, thermal fluctuation effects in fine magnetic crystallines is remarkable due to weak exchange coupling among crystal grains and the apparent coercive force is high resulting in that it was impossible to record on it accurately. Furthermore, even when recording is performed under a large current with utilization of a modified recording circuit, etc., the magnetic recording transition region is widened due to a broad magnetic recording field resulting in that noise increases and/or recorded information is lost when it was alowed to stand for a long time.
An object of the present invention is to provide a low-noise magnetic recording medium composed of fine crystal grains which is capable of recording and reading at a high data transfer rate of not less than 50 MB/s and further permits high-density recording at not less than about 5 Gb/in2, a recording and reading magnetic head with high reading sensitivity which is capable of sufficiently sharp recording on the medium, and a magnetic recording device of a high data transfer rate and high density which is realized by using the magnetic recording medium and the magnetic head of the present invention.
In order to achieve the above object, the present inventors pushed forward studies on chemical compositions of magnetic recording media, deposition processes and technologies related to devices such as magnetic heads, and found out that the following means are very effective.
There is proposed a magnetic recording medium with a magnetic layer comprising at least one metal element selected from the group consisting of Co, Fe and Ni as a primary component, at least two elements selected from a second group consisting of Cr, Mo, W, V, Nb, Ta, Ti, Zr, Hf, Pd, Pt, Rh, Ir and Si, and at least one element selected from a third group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Bi, Sb, Pb, Sn, Ge and B. According to the magnetic recording medium, it is possible to obtain a high S/N (signal-to-noise) ratio even under recording at high data transfer rate of not less than 50 MB/s and to reduce the absolute value of normalized noise coefficient per a unit transition {square root over (Nd2+L xe2x88x92No2+L )}xc2x7{square root over (Tw)}/(S0xc2x7D)(Nd: recorded media noise, No: DC erase noise, Tw: effective read track width, S0: isolated pulse output, D: recording density in the unit of flux change per inch) to not more than 2.5xc3x9710xe2x88x928 (xcexcVrms) (inch)(xcexcm)0.5/(xcexcVpp).
The invention can provide a magnetic recording device which can perform recording at a high data transfer rate of not less than 50 MB/s by using the above magnetic recording medium, a magnetic recording head and an R/W-IC having the following features; that is, the magnetic recording head assembly is given a total inductance reduced to not more than 65 nH because it has a magnetic core length of not more than 35 xcexcm, because it is provided with a magnetic film with a resistivity exceeding 50 xcexcxcexa9cm or a multilayer film composed of a magnetic film and an insulating film in part of the magnetic core, and further because it is mounted on an integrated circuit suspension; and the R/W-IC produced using a process of a line width of not more than 0.35 xcexcm and is capable of operating at high frequencies. Furthermore, the magnetic recording device of the present invention can perform the reading of magnetic information at a high density of not less than 5 Gb/in2 by using a magnetic head provided with a read element having a giant magnetoresistance effect or a tunneling-magnetoresistance effect and with an effective track width of not more than 0.9 xcexcm.
Recording density can be increased about 20% by forming the magnetic layer of the magnetic recording medium through a non-magnetic intermediate layer comprising at least one element selected from the group consisting of Cr, Mo, W, V, Nb, Ta, Zr, Hf, Ti, Ge, Si, Co, Ni, C and B as a primary component.
A magnetic recording and reading device of higher density can be provided by performing magnetic recording immediately after heat application to a magnetic recording medium through the use of a semiconductor laser, etc. and performing reading with the aid of the above giant magnetoresistance effect element or an element having a tunneling-magnetoresistive thin film.
Furthermore, in order to shorten an access time and perform positioning with higher accuracy, it is effective to adopt a rotary type actuator to position the head in at least two stages of coarse and fine movement adjustments.
The present inventors pushed forward on read-and-write properties of a magnetic recording medium as shown in FIG. 12, which is fabricated by forming a magnetic layer of a Co alloy, etc., a protective layer of Cxe2x80x94N, etc., and a lubricating layer of perfluoro-alkyl-polyether, etc., in this order, directly on a non-magnetic substrate or via a non-magnetic underlayer which comprises at least one element selected from the group consisting of Cr, Mo, W, Ta, V, Nb, Ta, Ti, Ge, Si, Co and Ni as a primary component, the above magnetic layer was formed by controlling film deposition conditions, such as substrate temperature, atmosphere and deposition rate, heat treatment conditions, compositions of magnetic layer or under layer, a thickness of each layer, crystalline, the number Cf layers, etc. At a recording density of 3 Gb/in2 and at 10 kprm, these magnetic media were evaluated through the use of a conventional magnetic head with the MR element as shown in FIGS. 11A and 11B on a conventional magnetic disk device as shown in FIGS. 10A and 10B. As a result, the present inventors found out that by giving the above magnetic layer of a composition containing at least one metal element selected from the group consisting of Co, Fe and Ni as a primary component, and at least two elements selected from a second group consisting of Cr, Mo, W, V, Nb, Ta, Ti, Zr, Hf, Pd, Pt, Rh, Ir and Si, it is possible to refine crystal grains and reduce the exchange interaction among crystal grains and also to reduce the absolute value of normalized noise coefficient per recording density to not more than 3xc3x9710xe2x88x928 (xcexcVrms) (inch) (xcexcm)0.5/(xcexcVpp) even when recording and reading are performed at a transfer rate of not more than 20 MB/s of conventional technology. This effect was remarkable especially during low-pressure, high-temperature and high rate film depositions or during film depositions at a high pressure and a low deposition rate. Under other conditions, however, this effect was good enough by optimizing compositions and combinations.
On the other hand, in order to record at a high rate of not less than 50 MB/s, it was necessary to use an R/W-IC (Read and Write IC) which is capable of a high speed processing by putting fine-pattern-width for not more than 0.35 xcexcm to partial use at least and, in addition, it was necessary to develop a magnetic recording head structure capable of generating a strong magnetic recording field at a high rate in response to this fast driving current. In order to prevent the deterioration of fast signals, it is important that the IC be installed in a position as close to the head as possible and it was desirable to reduce the distance to not more than 2 cm. The present inventors examined magnetic pole and head structures and materials for magnetic poles, and developed a magnetic head assembly with a total inductance reduced to not more than 65 nH in which the magnetic core length 11 of a magnetic recording core composed of the lower magnetic pole 118 and the upper magnetic pole 117 in FIG. 11A is not more than 35 xcexcm, and which is provided with a magnetic film with a resistivity exceeding 50 xcexcxcexa9cm or a multilayer film composed of a magnetic film and an insulating film in part of the magnetic poles composing the magnetic core, and which is mounted on a suspension 113 with an integrated conductive line through insulator 1116. Recording magnetic fields obtained by this magnetic head were evaluated with the aid of a magnetic field SEM, MFM, etc. As a result, the present inventors could ascertain that a sufficient magnetic field can be generated even at a data transfer rate of not less than 50 MB/s, and found out that recording at a transfer rate of not less than 50 MB/s is, in principle, possible. Materials for magnetic poles with a resistivity exceeding 50 xcexcxcexa9cm include, for example, NiFe-base alloys, such as 42Ni-57Fe-1Cr, 46Ni-52Fe-2Cr, 43Ni-56Fe-1Mo, 51Ni-47Fe-2S and 54Ni-43Fe-3P, and amorphous magnetic alloys, such as CoTaZr and CoNbZr. Examples of multilayer film composed of a magnetic film and an insulating film include a multilayer film composed of 89Fe-8Al-3Si and SiO2 and a multilayer film composed of 80Ni-20Fe and ZrO2.
When recording and reading on the above medium at 50 MB/s through the use of the magnetic head and circuit of the above construction, satisfactory recording was incapable due to a bad overwrite characteristic, etc. and besides noise increased twice or three times. Thus, it became apparent that further ideas are necessary for ensuring recording and reading both in high-density and high data transfer rate. Here, signals were read through the use of a conventional MR read element with a narrow track width of 2 xcexcm.
The reason for the above phenomenon was examined. The present inventors considered that the above phenomenon is due to a bad frequency response in the recording characteristic of the medium. Therefore, the cause was analyzed by performing a simulation through the use of a super computer, etc. and as a result, it became evident that there is a problem in thermal fluctuations of magnetization and spin damping during recording process. Therefore, studies were carried out on medium additives capable of optimizing thermal fluctuations and damping coefficient. As a result, the present inventors found out that by adding at least one element selected from a third group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Bi, Sb, Pb, Sn, Ge and B to the composition of the above medium, it is possible to reduce the absolute value of normalized noise coefficient per recording density to not more than 2.5xc3x9710xe2x88x928 (xcexcVrms) (inch) (xcexcm)0.5/(xcexcVpp) even when recording is performed at 50 MB/s. This effect was observed when the above elements were added in amounts of not less than 0.1 at %. However, their addition in an amount of 0.1 at % is sufficient. Addition in amounts of not more than 0.1 at % was undesirable because of a remarkable decrease in output. Furthermore, the effect was remarkable when rare earth elements were added. The above effect was also ascertained in what is called a granular type medium in which a non-magnetic substance, such as SiO2 and ZrO2, and a magnetic material with a high crystalline anisotropy constant, such as CoPt and CoNiPt, were simultaneously formed by sputtering and the magnetic material with a high crystalline anisotropy constant was precipitated and dispersed by heat treatment at a temperature of about 300xc2x0 C. to obtain the above composition. Furthermore, in a case where the above magnetic layer is made of an amorphous magnetic substance, the magnetic layer often has perpendicular anisotropy. However, the same effect was also observed in this case. Furthermore, in any of these instances, when the above magnetic layer was formed via a non-magnetic intermediate layer containing at least one element selected from the group consisting of Cr, Mo, W, V, Nb, Ta, Zr, Hf, Ti, Ge, Si, Co, Ni, C and B as a primary component, noise could be remarkably reduced because of statistical addition of signals and this was especially favorable for noise reduction. Furthermore, what is especially noteworthy is that by reducing the magnetic core length of the above magnetic head to not more than 50 xcexcm, a sharp and strong magnetic field could be generated with increased efficiency and recording on a medium with a higher coercive force was possible. This is preferable because higher densities can be obtained. Furthermore, by installing the above R/W-IC near the suspension, the rise time of a recording magnetic field could be made further shorter. This permitted sharp recording and enabled medium noise to be relatively reduced. Therefore, this is more preferable.
In order to perform recording and reading at a high density of not less than 5 Gb/in2, it was necessary to perform the reading of magnetic information through the use of a magnetic head having an effective read-track width of not more than 0.9 xcexcm with giant magnetoresistive effect or tunneling-magnetoresistive effect, and performs the reading of magnetic information at a high density of not less than 5 Gb/in2. By performing reading like this, a signal-to-noise ratio of not less than 20 dB of the device necessary for the operation of the device was obtained with the aid of the signal processing method and it was necessary to combine the magnetic head with signal processing such as EPRML or EEPRML, trellis coding, ECCs, etc. Incidentally, the giant magnetoresistive element (GMR) and tunneling magnetic head technologies are disclosed in JP-A-61-097906, JP-A-02-61572, JP-A-04-35831, JP-A-07-333015, JP-A-02-148643 and JP-A-02-218904. An effective track width of not more than 0.9 xcexcm was realized by putting lithography technology based on an i-line stepper or a KrF stepper, FIB fabrication technology, etc. to full use.
The above system was a very epoch-making product as a magnetic disk. However, the present inventors found out that recording can be assisted by instantaneously heating a medium to the temperature range of from about 50xc2x0 C. to 250xc2x0 C. with a magnetic disk provided with a heat-generating portion and thereby reducing the coercive force at a high frequency, and that this idea is further effective. In other words, in this system the load put on the recording portion and the material for recording magnetic poles could be reduced, and recording at a high density of not less than 5 Gb/in2 and a high data transfer rate of not less than 50 MB/s was possible even with a recording track width of not more than 0.9 xcexcm and even when a magnetic pole material with a saturation magnetic flux density of 1 T was used. Thus, this was especially advantageous.
With respect to this effect, access time can also be shortened by performing magnetic recording immediately after heat application to a magnetic recording medium and performing reading with the aid of the above giant magnetoresistive element or element having a tunneling-magnetoresistive effect. This is further preferable.
Furthermore, by using a semiconductor laser chip as the above heat-generating portion, an effective head volume can be reduced and high-speed positioning becomes possible. This is especially preferable. In addition, in order to shorten access time and ensure positioning with a higher accuracy, it is especially effective to position the head by a rotary actuator method in at least two stages of coarse and fine movement adjustments.